1. Field of the Invention
The present invention relates to an optical information recording medium, and more particularly to an optical information recording medium comprising a transparent substrate such as a transparent disc on which a recording layer, a reflection layer, a hydrophobic protective layer, a hydrophobic intermediate layer, and an ink receiving layer are successively overlaid, on which ink receiving layer clear printing can be performed, using an ink, for instance, by means of ink jet printing or screen printing, regardless of the color of the ink employed.
2. Discussion of Background
Optical information recording media have been widely used in the fields of audio equipment, information processing and the like, as reproduction-only type optical information media or as write once read many type (WORM type) optical information media, such as CD, CD-R, DVD-R, DVD-ROM, CD-RW and DVD-RW.
These optical information recording media are composed of a transparent substrate made of a material such as glass or plastics, and an optical recording layer or a magneto-optical recording layer which is overlaid on the substrate.
Generally, in these optical information recording media, a recording layer, a reflection layer and a protective layer are successively formed and overlaid on a doughnut-shaped, transparent substrate disc by spin coating or sputtering.
The recording layer is generally a resin layer which contains an organic pigment such as a cyanine pigment or phthalocyanine pigment. Information is recorded on the recording layer, and recorded information is reproduced therefrom by applying a laser beam with a wavelength of 770 to 790 nm to the recording layer through the transparent substrate.
The reflection layer is generally formed on the recording layer, for example, by sputtering. The reflection layer is formed in the shape of a thin film, and is made of a metal, such as Au or Al, that can efficiently reflect the laser beam which has passed through the recording layer.
Furthermore, a protective layer made of a resin film is overlaid on the reflection layer in order to protect the recording layer and the reflection layer from physical or mechanical adverse effects produced, for example, by the substrate.
Generally, these optical recording media include an index display indicating the contents of recording as well as various designs for the optical recording media, which are printed on the surface of the protective layer. When a large number of the optical recording media is produced and therefore the index display and the various designs are mass printed, the printing is generally carried out by transfer printing, such as screen printing, pad printing, and offset printing.
In the case where the number of optical recording media made is relatively small, for example, as in the case of self-made CD, promotion CD, audition CD, or test CD, the contents of recording thereof could be reproduced and confirmed by means of a CD player, but the above-mentioned printing of the contents of recording will be more convenient and therefore is required. Furthermore, in accordance with the wide spread use of write-once type optical information recording media including CD-ROM for personal computers, the customer can make his or her own CD-ROMs, although the number is relatively small. For such customer's own CD-ROMs, there is a demand for printing the contents of recording.
Under such circumstances, it is required that the indexes indicating the contents of recording and other designs be on the surface of the protective layer or a printing surface of a label before or after information is recorded on the recording medium.
In accordance with the above-mentioned demand, for example, Japanese Laid-Open Patent Application 6-60432 proposes an optical information recording medium comprising (1) a protective layer, which is usually hydrophobic, and has been worked so as to have a roughened surface, and (2) a hydrophilic resin layer serving as a printing layer on which the above-mentioned printing can be performed, which is provided on the protective layer, whereby printing can be performed, using an aqueous ink, on the hydrophilic resin layer formed on the protective layer.
In the above proposal disclosed in Japanese Laid-Open Patent Application 6-60432, it is intended to perform printing on the hydrophilic resin layer serving as the printing layer, using an aqueous ink, since the protective layer is usually a hydrophobic resin layer which is not suitable for printing with the aqueous ink.
However, it is generally considered to be difficult to form the hydrophilic resin layer on the hydrophobic protective layer in close contact with one another in view of the repelling properties of the two layers like an oil and water. In other words, it is considered to be difficult to form a stable hydrophilic resin layer which serves as an image fixing layer for the aqueous ink on the hydrophobic protective layer.
As can be clearly noted from the above proposal, when the surface of the protective layer is subjected to surface-roughening working to improve the matching and adhesion between the protective layer and the hydrophilic layer, complicated steps are required to be conducted, such as coating a hydrophilic resin on the protective layer before the protective layer is completely cured.
Furthermore, in the above proposal, even if the printing has been carried out using the aqueous ink, the complicated steps such as subjecting the protective layer to the above-mentioned surface-roughening treatment and forming the hydrophilic resin layer on the hydrophobic surface of the protective layer are required to be conducted, but there remains a problem in the adhesion between the protective layer and the hydrophilic layer. In short, a sufficiently stable ink fixing layer for use in practice has not yet been proposed.